In this article we will discuss about the Circulatory System in Cockroach:- 1. Subject Matter of Circulatory System in Cockroach 2. Circulating Fluid in Cockroach 3. Mechanism.

Subject Matter of Circulatory System in Cockroach:

Cockroach being an insect possesses an open circulatory system.

The system is poor­ly developed and consists of following organs:

Heart and Aorta:

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The heart of cockroach is an elongated contractile, narrow tube lying along the mid-dorsal line of thorax and abdomen just beneath the terga. The heart is enclosed in a pericardial sinus, the wall of which has segmented bundles of alary mus­cles and a dorsal fenestrated diaphragm.

The wall of the heart is composed of outer con­nective tissue and median muscle cells. The cavity of the heart is lined by the sarcolemma of median muscle cells. The heart consists of thirteen funnel-shaped and segmentally arranged chambers, each communicating by a valvular opening with that lying in front of it (Fig. 2.65).

Structure of Heart of Periplaneta Americana

The hinder end of each chamber has a pair of minute, lateral and valvular openings called ostia, which allows the flow of blood from the pericardium into the heart only and not in reverse direction. In each seg­ment, heart sends a pair of ex-current arteries.

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The heart is closed behind but is continued forward as a short and narrow tube without ostia called the aorta. This aorta and segmen­tal arteries finally open within the haemocoelic spaces.

Haemocoel:

The body cavity of cock­roach is not a true coelom but a haemocoel containing blood (haemolymph).

The diaphragm or the dorsal fenestrated partition divides the haemocoel into three sinuses:

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(i) The dorsal or pericardial sinus surroun­ding the heart, aorta and alary muscles,

(ii) The middle or perivisceral sinus contai­ning the alimentary canal (Fig. 2.66) and

(iii) The ventral sternal or perineural sinus enclosing the ventral nerve cord. It also extends into the legs as septa, dividing the cavity of each leg into two sinuses, one for the outward and the othe